[syzbot ci] Re: Improve khugepaged scan logic

[syzbot ci <syzbot+ci74fd370f54089b9b@syzkaller.appspotmail.com>]

syzbot ci has tested the following series

[v2] Improve khugepaged scan logic
https://lore.kernel.org/all/20251229055151.54887-1-yanglincheng@kylinos.cn
* [PATCH v2 1/4] mm: khugepaged: add trace_mm_khugepaged_scan event
* [PATCH v2 2/4] mm: khugepaged: just skip when the memory has been collapsed
* [PATCH v2 3/4] mm: khugepaged: set VM_NOHUGEPAGE flag when MADV_COLD/MADV_FREE
* [PATCH v2 4/4] mm: khugepaged: set to next mm direct when mm has MMF_DISABLE_THP_COMPLETELY

and found the following issue:
WARNING in madvise_dontneed_free

Full report is available here:
https://ci.syzbot.org/series/f936dff1-2423-4f46-a59a-ea041c1d741a

***

WARNING in madvise_dontneed_free

tree:      mm-new
URL:       https://kernel.googlesource.com/pub/scm/linux/kernel/git/akpm/mm.git
base:      33b485bade996a9d0154cf0888b7a5c23723121e
arch:      amd64
compiler:  Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
config:    https://ci.syzbot.org/builds/81f62216-5094-4281-a942-238b7448a3be/config
C repro:   https://ci.syzbot.org/findings/e308c3a0-c806-45c4-bc1c-24536a3c3ca3/c_repro
syz repro: https://ci.syzbot.org/findings/e308c3a0-c806-45c4-bc1c-24536a3c3ca3/syz_repro

------------[ cut here ]------------
WARNING: mm/madvise.c:795 at get_walk_lock mm/madvise.c:795 [inline], CPU#0: syz.0.17/5977
WARNING: mm/madvise.c:795 at madvise_free_single_vma mm/madvise.c:830 [inline], CPU#0: syz.0.17/5977
WARNING: mm/madvise.c:795 at madvise_dontneed_free+0xb52/0xe10 mm/madvise.c:960, CPU#0: syz.0.17/5977
Modules linked in:
CPU: 0 UID: 0 PID: 5977 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:get_walk_lock mm/madvise.c:795 [inline]
RIP: 0010:madvise_free_single_vma mm/madvise.c:830 [inline]
RIP: 0010:madvise_dontneed_free+0xb52/0xe10 mm/madvise.c:960
Code: c7 c6 b0 6e 25 8e e8 7d 4c a3 ff 48 83 fb 01 74 0c 83 fb 03 75 0e e8 ed 46 a3 ff eb 12 e8 e6 46 a3 ff eb 09 e8 df 46 a3 ff 90 <0f> 0b 90 31 db 89 9c 24 08 01 00 00 48 8b 74 24 68 48 8b 54 24 70
RSP: 0018:ffffc90004a17400 EFLAGS: 00010293
RAX: ffffffff821e7411 RBX: 0000000000000002 RCX: ffff888169b7d7c0
RDX: 0000000000000000 RSI: ffffffff8e256eb0 RDI: 0000000000000002
RBP: ffffc90004a175b0 R08: ffff888169b7d7c0 R09: 0000000000000002
R10: 0000000000000003 R11: 0000000000000000 R12: 0000000000000000
R13: dffffc0000000000 R14: 0000000000000100 R15: 1ffff92000942e88
FS:  0000555555761500(0000) GS:ffff88818e62f000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fe49d72b600 CR3: 00000001b85b6000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 madvise_vma_behavior+0xd57/0x3680 mm/madvise.c:1385
 madvise_walk_vmas+0x575/0xaf0 mm/madvise.c:1730
 madvise_do_behavior+0x38e/0x550 mm/madvise.c:1944
 do_madvise+0x1bc/0x270 mm/madvise.c:2037
 __do_sys_madvise mm/madvise.c:2046 [inline]
 __se_sys_madvise mm/madvise.c:2044 [inline]
 __x64_sys_madvise+0xa7/0xc0 mm/madvise.c:2044
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe49d78f7c9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff39cea178 EFLAGS: 00000246 ORIG_RAX: 000000000000001c
RAX: ffffffffffffffda RBX: 00007fe49d9e5fa0 RCX: 00007fe49d78f7c9
RDX: 0000000000000008 RSI: 0000000000600002 RDI: 0000200000000000
RBP: 00007fe49d7f297f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe49d9e5fa0 R14: 00007fe49d9e5fa0 R15: 0000000000000003
 </TASK>


***

If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
  Tested-by: syzbot@syzkaller.appspotmail.com

---
This report is generated by a bot. It may contain errors.
syzbot ci engineers can be reached at syzkaller@googlegroups.com.